U.S. PATENT DOCUMENTS
U.S. Pat. No. 3,766.745 by inventor Lester K. Quick
U.S. Pat. No. 4,014,182 by inventor Eric Granryd
1. Field of the Invention
This invention pertains to a novel liquid vapor refrigeration cycle which evaporates the liquid leaving the condenser by thermally-isolating the liquid from energy loss during the evaporative cooling of the liquid as it is cooled below the condensing temperature by an evaporative engine. This allows a refrigerator to achieve efficiency greater than has been achieved in the past by evaporative cooling of the warm liquid and powering an evaporative engine, and as a result of its greater efficiency it is also possible to achieve lower temperatures than before.
2. Description of the Related Art
Most prior art liquid-vapor refrigerant systems have attempted to eliminate the energy wasted during expansion of the liquid across an expansion valve by incorporating expansion engines, or have attempted to continuously remove the energy in the warm condensate liquid with an auxiliary refrigeration system which is continuously operating at a higher coefficient of performance. The expansion engines have not recognized that the expansion must be done in a reversible manner and also have the disadvantage that the expanded refrigerant must then be recompressed by the compressor at a lower COP (coefficient of performance). Mechanically sub-cooled systems have the added disadvantage that they have losses due to expansion valves and the heat exchanger.
U.S. Pat. No. 3,766,745 by inventor Lester K. Quick describes an invention that overcomes the need for a heat exchanger to cool the warm liquid at a better COP (coefficient of performance). However, U.S. Pat. No. 3,766,745 still has the major disadvantage of prior art systems of irreversible free expansion into a tank and at the expansion valves, which causes the major inefficiency in the Quick invention and all other liquid vapor prior art systems. U.S. Pat. No. 3,766,745 also utilizes expansion valves at the evaporators, which also result in the irreversible free expansion of the refrigerant. This system allows energy exchange from the liquid being expanded and the liquid and gas molecules which have gone through the expansion. This means that the potential energy which is in the liquid is wasted by accelerating molecules randomly. This is a consequence of the liquid not being thermally-isolated during the expansion process.
U.S. Pat. No. 4,014,182 by inventor Eric Granryd describes an invention, which contains an evaporator, a condenser, a compressor and a closed vessel which receives condensed refrigerant from the condenser. The vessel has outlets connected to the compressor and to the evaporator. Communication between the vessel and the compressor is established for a regulated period to lower the pressure in the vessel, causing the refrigerant therein to boil and cool. During most of this period, communication between the evaporator and the compressor is closed and thereafter is opened. This patent uses a batch process to cool the warm refrigerant.
U.S. Pat. No. 4,014,182 does address the problem of irreversibility at the expansion valve and offers a solution which, however, introduces several other irreversibilities, and hence inefficiencies, into the system that have not been previously recognized. One of the irreversibilities introduced by Granryd comes about in the vessel, which contains the evaporating refrigerant. The refrigerant is placed in the vessel and refrigerated. As it cools, it also cools the walls of the vessel. When the cool liquid is ejected and the next batch of warm liquid is placed into the vessel, the vessel is at a low temperature and the energy from the warm liquid flows from the refrigerant into the walls. Thus, the previous liquid cooling cycle was used to remove part of the energy in the injected warm liquid refrigerant at a lower COP than would be possible if the transfer of energy from the vessel walls had not taken place. Since the cost of removing the energy at the end of the cycle is the greatest, this means that the portion of the cycle, which would benefit the most from this approach, is actually costing the most. Also, some of the vapor from the condenser condenses on the cool walls of the vessel, which actually adds more heat load to the refrigeration system; this is also an additional irreversible process. Thus, if appreciable energy exchange is allowed to take place between the liquid and the cooling vessel surroundings, the process is made more irreversible and thus more inefficient. It is therefore, important to minimize the relative amount of energy which is transferred in and out of the liquid before, during, and after the liquid cooling process, as is disclosed in the present invention.
In the current invention the liquid is allowed to expand reversibly by evaporative cooling in a container from which the liquid is thermally-isolated. The evaporative cooling process is used to power an engine. The cooled liquid is then delivered to the evaporator for cooling a cooled substance without the need of an expansion throttling valve, or the pressure reducing device of U.S. Pat. No. 3,766,745, or the heat exchangers used in sub-cooling systems.
Several types of expansion engines are disclosed for use in the invention. The limitation of showing a number of engines is present due to the impracticality of showing each and every type of expansion engine which could be powered by this method and is not intended to limit the invention to the engines disclosed. One new and novel engine compressor is disclosed which combines the process of an engine and compressor in a standard compressor which has been modified to accommodate the novel thermal-isolative cooling process.
Thermally-isolative cooling process is the process of minimizing energy flow from the condensate liquid during the period which it is cooled in a cooling vessel. This means that the amount of energy flowing to or from the liquid as the result of contact with its surroundings, per unit mass of refrigerant circulated, should be small during this process in order to obtain a high efficiency.
The problem of losing energy from the liquid when it enters the liquid cooling container because the cooler is cold from the previous cycle was not recognized by Granryd in U.S. Pat. No. 4,014,182. Neither was the problem of vapor entering the cooling vessel from the condenser and condensing on the cool walls of the cooling vessel, thereby adding energy to the cycle and causing the compressor to remove more energy than a conventional refrigeration cycle. Therefore, the solution of providing a thermally-isolated inner surface for the liquid cooling container, which would isolate the liquid thermally from the cooling vessel and limit the energy exchanged with the liquid, was not proposed by Granryd. Granryd did propose the use of insulation on the tank but did not teach the use of thermal-isolation of the liquid within the container, i.e., the liquid has to be thermally-isolated against the flow of energy to or from the cooling vessel during the reversible process of evaporation. If it is not thermally-isolated the process will not be reversible and, thus, will be more inefficient.
One embodiment of the current invention solves the problems presented by the Granryd patent by replacing the liquid cooling vessel with a container, which thermally-isolates the liquid refrigerant from its surroundings during the liquid cooling process. This eliminates the irreversible free expansion that has taken place in most prior art systems and replaces it with a reversible expansion process, which achieves a higher efficiency. It also eliminates the irreversible transfer of energy from the liquid to the surroundings by thermally-isolating the liquid from the container by using a thermally minimally conducting liner. Irreversible expansion which was present in U.S. Pat. No. 4,014,182 due to the thermal conduction between the vessel used to expand the refrigerant and the refrigerant is eliminated in the current invention. The current invention also eliminates the problem in U.S. Pat. No. 4,014,182 of vapor condensation on the cool walls of the cooling vessel, which took place during part of the cycle.
Tests on a system constructed in accordance with U.S. Pat. No. 4,014,182 indicate that the operational cost of a system constructed in this way will exceed the cost of operation of a conventional refrigeration system which is equipped with an expansion valve. This could explain why such a system has not achieved commercial success in the 22 years since the issuance of U.S. Pat. No. 4,014,182. The current invention demonstrates the solution to a long felt need by discovering and solving the problems of inefficiency in refrigeration systems, which have gone unrecognized for those 22 years.
The current invention also solves the problem of moving the liquid from the condenser to the liquid cooling container and then to the evaporator. This problem was not recognized previously, and therefore, no solutions exist to this problem in the prior art.
Finally, the problem of irreversibility at the expansion valve in a liquid vapor system has not been solved successfully prior to this invention. A common attempt in the past to overcome the inefficiency due to the irreversible nature of the expansion through the expansion valve has been to utilize the energy that is lost by running an engine with the wasted energy. These common attempts fail to utilize a thermally-isolative cooling process and are as a consequence less efficient than the process disclosed currently. The solution utilized in one embodiment currently disclosed utilizing the expansion engine compressor, and in another utilizing an expansion engine, offers greater efficiency than can be achieved by the expansion engine solution because it is a more reversible process. This is because of the use of the more reversible process of thermally-isolating the warm refrigerant during the cooling process. This means that the inefficiency of the engine is magnified by inefficiency of the compressor resulting in an efficiency less than the current invention.